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Discussion Starter #1
i was wondering how much i can bore out my 402
took the heads off today and the one cylinder had tons of water and was rusted pretty bad... so im wondering if i can do another .30 over? and do they make pistons that will fit once its bored out this much more? anything else ill need to replace?
 

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Cast and Hyper pistons are made in Standard size as well as a 0.020", 0.030", 0.040", and 0.060" normal production overbore pistons that are sitting on the shelf awaiting your order. Forged pistons are on the shelf only as a 0.030" or a 0.060" over bore size. The piston companies will make pistons in any size you want (pro stock engine builders buy custom pistons in an over bore of 0.002" at a time and have for or five incremental increases in bore sets ready to drop into a block as it wears to maintain a tight seal.

As for as your 402 block it can be safely over bored 0.060" (and even then you should check it for core shift first). If while you are sonic checking the block you discover that the core shift for all eight pistons happens to fall onto the thrust side of the block you could take it out as far as 0.100" over and still not have a cylinder that shimmies as the piston moves down the bore due to deflection of a thin cylinder wall. A partial block fill helps the bottom of the bore stability with a motor over bore like that; but expect the block to run hot. It runs hot not because it is half full of concrete, but because the cylinder walls are so thin that they glow red from the cylinder heat escaping into the coolant because of thermal transport through the thinner cast iron. That lost heat, is lost power.

Big Dave
 

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Discussion Starter #3
awesome thanks alot! i will only do the .30 over the factory bore. just wanted to make sure i can since its already been bored in the factory
shes just rusted out inside so all i wanna do is get rid of the rust so i can get the engine working
 

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Chevrolet opened up the molds when casting the block to make the 0.030" over the stock 396 bore. It still has the full 0.060" of metal for over boring.

Chevrolet just had to break the 400 cube barrier for marketing reasons because all of Chevy's competitors; including within GM, as well as the blue oval boys and MOPAR efforts that had motors with 400 cubes or more available in small and mid sized cars. So the 396 became a 402 and the 427 jumped to 454 (Even though every other engine in GM's line up had a 455 engine size as their top dog except for Cadillac that had a 400 horsepower 500 cube torque monster).

Big Dave
 
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